Field of the Disclosure
The present disclosure relates to a method of driving an organic light emitting diode display device and, more particularly, to a method of driving an organic light emitting diode display device where sub-pixels for displaying an image are determined according to a gray level.
Discussion of the Related Art
Recently, as information technology has progressed, display devices have rapidly advanced. Among the advances is a flat panel display (FPD) having an excellent performance, such as a thin profile, a light weight and a low power consumption. In particular, a liquid crystal display (LCD) device and an organic light emitting diode (OLED) display device have been widely used.
The OLED display device of an emissive type has advantages such as a simple fabrication process, a thin profile and a light weight as compared with the LCD device requiring a backlight unit as an additional light source. Also, the OLED display device has an excellent viewing angle and an excellent contrast ratio as compared with the LCD device. Further, the OLED display device is driven with a direct current (DC) low voltage due to the low power consumption. As a result, a driving circuit is easily fabricated and designed. Moreover, since inner elements of the OLED display device are formed of solid build, the OLED display device has advantages such as excellent durability against an external impact and a wide temperature range of operation.
The OLED display device has been researched for a wider application range according to user's various demands. For example, the OLED display device has been utilized as a monitor of a desktop computer and a wall-mountable television as well as a portable computer. The OLED display device having a larger display area also has been researched.
The OLED display device displays an image using three primary colors such as red, green and blue. Recently, the OLED display device has displayed an image using four colors such as red, green, blue and white to increase brightness and decrease power consumption.
FIG. 1 is a graph illustrating a luminance according to a gray level of an organic light emitting diode display device having red, green, blue and white sub-pixels according to the related art. FIG. 2 is a graph illustrating a luminance ratio according to a gray level of an organic light emitting diode display device having red, green, blue and white sub-pixels according to the related art. FIG. 3 is a graph illustrating a data voltage according to a gray level of an organic light emitting diode display device having red, green, blue and white sub-pixels according to the related art.
With reference to FIG. 1, when a white image is displayed using red, green, blue and white sub-pixels, most luminance is expressed by the white sub-pixel and the other luminance for adjusting a color corresponding to a required color temperature is expressed by the red, green and blue sub-pixels.
With reference to FIG. 2, for example, when a white image having a luminance ratio of about 100% is displayed, the white sub-pixel expresses a luminance ratio of about 80% and the red, green and blue sub-pixels express a luminance ratio of about 20%. Accordingly, as a gray level increases, a data voltage for driving a light emitting diode of the white sub-pixel increases.
With reference to FIG. 3, for example, although the data voltage of the red, green and blue sub-pixels for a 255th gray level is about 4V, the data voltage of the white sub-pixel for a 255th gray level is about 16V.
As a result, the red, green and blue sub-pixels of the four sub-pixels are driven with a lower data voltage as compared with the white sub-pixel of the four sub-pixels and as compared with the red, green and blue sub-pixels of the three sub-pixels.
However, since the data voltage of the red, green and blue sub-pixels is reduced, luminance uniformity of a display panel is reduced due to a noise when a relatively low gray level is expressed. For example, as illustrated in FIG. 3, although the data voltage of the white sub-pixel for a 96th gray level is about 6V, the data voltage of the red, green and blue sub-pixels for a 96th gray level is about 2V.
FIG. 4 is a graph illustrating a fluctuation of a data voltage due to a noise of an organic light emitting diode display device according to the related art. FIG. 5 is a picture illustrating a non-uniformity in luminance when a relatively low gray level is expressed by an organic light emitting diode display device according to the related art.
With reference to FIG. 4, the data voltage of an OLED display device including the three sub-pixels is a first voltage V1, and the data voltage of an OLED display device including the four sub-pixels is a second voltage V2 smaller than the first voltage V1. The data voltage of the second voltage V2 is vulnerable to noise as compared with the data voltage of the first voltage V1. The noise may be caused by a coupling such as a kick-back phenomenon due to a load between a transistor and a gate line or by an external circuit.
With reference to FIG. 5, when an image of a relatively low gray level displayed by the display panel has poor luminance uniformity, a linear stain is shown due to high and low luminance portions.